A window wall system which in general, spans from the top surface of a floor to the underside of the floor above or to the bottom edge of a spandrel masonry or concrete panel above. Most of the window wall systems in the market include four types of wall components, namely, (1) a bottom sealing and anchoring member, (2) a top sealing and anchoring member, (3) shop prefabricated panel units installed between the bottom and the top anchoring members, and (4) an exterior floor slab cover. The parameters for a successful window wall project include durable weather shield, durable structural safety, ability to adjust for construction tolerances of the wall anchoring surface, easiness of erection, and no need for exterior access or lifting equipment. Any improvement on these parameters would represent an advance in the window wall technology. In addition, the ability to maintain a curtain wall type of flush exterior appearance is highly desirable but rather difficult since the window wall must be supported on the floor while the water infiltrated into the wall panel joints must be drained to the exterior of the slab edge making it become necessary for the slab edge cover to be protruded from the face of the window wall. Through years of experiences, the major areas needing further improvement are described as follows:                (1) Water-tightness Performance: All conventional window wall systems require perfect sealing property at some critical sealing locations to maintain water-tightness performance. Experience indicated that the durability of the perfect sealing property at the critical seal locations is grossly inadequate due to workmanship and material degradation problems as well as stress fatigue due to various structural movements.        (2) The erected window wall is expected to be plumb and leveled at the design position. However, a ±¾″ (19 mm) variation in the finished floor level as well as the floor edge location are normally considered as acceptable in the building industry. In installing each piece of the top or the bottom anchoring member in a conventional window wall system, shims as required are used to adjust it to the design location. These anchoring members are continuous along the foot print of the window wall and they can be field cut to fit at a wall terminating end or at a wall corner, there is no need for the positioning adjustment in the left-to-right direction. Thus, before the anchoring screws can be applied, the anchoring member must be adjusted to both the true in-and-out position and the true up-and-down position by using shims as required. The application of an anchoring screw requires two steps, namely pre-drilling the screw hole using a driller and applying the screw using a screw gun. In both steps of the screw application, the anchoring member is very easy to slide on top of the shims causing it to be out of position and the shims are very easy to shift out of position, therefore, it is a very time consuming process to achieve the required quality result. In addition, the structural strength of the anchoring screw would be reduced with a high shim condition. Even though a reduced screw strength can be theoretically compensated by a reduced screw spacing at the high shim locations, it can't be shown on the drawing since the high shim locations can't be predefined and it is totally impractical to execute in the field without a pre-engineering calculation. It is most likely to compromise the structural integrity of the erected window wall. Even though the required screw spacing can be conservatively engineered with the assumption of highest shim condition, it would significantly increase the cost.        (3) In a conventional window wall system, each panel has a male jamb member and a female jamb member. The panels are erected in a fixed direction by engaging the male jamb into the female jamb of the already installed panel or vise versa. Due to the directional erection requirement, project delays are commonly caused by inadequate coordination with other trades on the job.        (4) In a conventional window wall system, the exterior floor slab edge cover and some exterior perimeter caulking lines are normally applied from outside after the panel erection. This exterior access requirement has a significant impact on the erection cost especially in a congested inner city location.        (5) An exterior wall system known as a Hybrid System represents an attempt to utilize the advantage of a window wall system for being supported between two adjacent floors and the advantage of a curtain wall system for flush exterior wall surface appearance. Experiences indicated multiple difficulties with anchoring and construction tolerance problems due to the notched mullion with discrete anchoring locations.        
Therefore there is need for an improved window wall system that overcomes the disadvantages of conventional wall systems.